Optical element and display device using the same

ABSTRACT

An optical element including a first pattern is provided. The first pattern includes a plurality of light deflection regions arranged along at least one set of first tracks in a first direction, and each first track is a waveform track having a first period T 1  and a first amplitude A 1 .

This application claims the benefit of Taiwan application Serial No.106114904, filed May 5, 2017, the disclosure of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The disclosure relates in general to an optical element and a display,and more particularly to an optical element for deflecting the light anda display device using the same.

BACKGROUND

The current display includes many structures arranged periodically witha regular period. If the micro-structures of the optical film disposedon the display have a pre-determined period, two periodic structureshaving different periods may generate a moiré interference pattern,which severely affects the display quality. Therefore, it has become aprominent task for the industries to develop an optical film without themoiré interference pattern issue.

SUMMARY

The disclosure is directed to an optical element and a display deviceusing the same capable of eliminating the moiré interference patternformed from the interference between periodically arranged structures.

According to one embodiment, an optical element including a plurality oflight deflection regions arranged along at least one set of first tracksin a first direction is provided. Each first track is a waveform trackhaving a first period T₁ and a first amplitude A₁.

According to another embodiment of the invention, an optical elementincluding a film and a plurality of light deflection regions isprovided. The light deflection regions are arranged on the film, andeach light deflection region comprises diffraction structures having twoor more than two types of periods.

According to an alternate embodiment of the invention, a display deviceis provided. The display device includes a display and an opticalelement disposed on a light output surface of the display.

The above and other aspects of the invention will become betterunderstood with regard to the following detailed description of thepreferred but non-limiting embodiment(s). The following description ismade with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of an optical element and a displaydevice using the same according to an embodiment of the invention.

FIG. 1B is a schematic diagram of four implementations of an opticalelement.

FIGS. 2A and 2B respectively are schematic diagrams of the lightdeflection regions arranged along the tracks in a first direction and anenlarged view of a region S₁.

FIGS. 3A and 3B respectively are schematic diagrams of the lightdeflection regions arranged along the tracks in a first direction and asecond direction and an enlarged view of a region S₂.

FIGS. 4A and 4B are schematic diagrams of two sets of light deflectionregions arranged along the tracks.

FIGS. 5A and 5B are schematic diagrams of the intersection of two setsof light deflection regions arranged along the tracks.

FIGS. 6A and 6B are schematic diagrams of three sets of partlyoverlapped light deflection regions arranged along the tracks.

FIG. 7A is a schematic diagram of a diffraction structure having asingle period.

FIGS. 7B-7E are schematic diagrams of diffraction structures having twoor more than two periods.

FIGS. 8A-8C are side views of diffraction structures having gradientperiods (or gradient densities) and gradient amplitudes.

FIGS. 9A-9D are FWHM (full width at half maximum) diagrams of fourdifferent types of diffraction structures.

DETAILED DESCRIPTION

A number of embodiments are disclosed below for elaborating theinvention. However, the embodiments of the invention are for detaileddescriptions only, not for limiting the scope of protection of theinvention.

Refer to FIG. 1A. The display device 1 includes a display 10 and anoptical element 20. The optical element 20 is disposed on a light outputsurface of a display 10 for displaying an image. The display 10 can be aliquid crystal display, a plasma display, an organic light-emittingdiode (OLED) display, an electronic paper display or other display fordisplaying an image. Meanwhile, the display 10 can be combined withother element. For example, the display 10 can be combined with a touchelement to form a touch panel. The optical element 20 and other element(such as an anti-reflection film or a touch panel) can be disposed onthe light output surface of the display 10.

The optical element 20 can be realized by a film having deflectionstructures for deflecting the light emitted by the display 10. Based onthe principles of the spherical coordinate system, two mutuallyperpendicular lines on a plane parallel to the display surface of thedisplay 10 are defined as coordinate axes. Normally, the horizontal linedirected rightward is defined as the X axis, the vertical line directedupwards is defined as the Y axis, and the axis perpendicular to thedisplay surface of the display 10 is defined as the Z axis. Thus, theobservation angle for watching the display 10 is represented by a zenithangle θ and a directional angle ψ of the spherical coordinate system,wherein, the directional angle ψ is formed by an angle with respect tothe X axis on the XY plane and can range from 0° to 360°; the zenithangle θ is formed by an angle with respect to the Z axis and can rangefrom +90° to −90°. Any two directions can form an angle. The anglerepresented by an anti-clockwise direction is a positive angle, and theangle represented by a clockwise direction is a negative angle. In anembodiment, the axial line parallel to the horizontal line can bedefined as the X axis, the axial line parallel to the vertical line canbe defined as the Y axis, and the third dimension perpendicular to theXY plane can be defined as the Z axis.

Refer to FIGS. 1A and 1B. In an embodiment, the optical element 20includes at least one light deflection region and an ordinary regionother than the light deflection region (a non-light-deflection region).When the light passing through the light deflection region at a specificdirection, high deflection effect will be generated. High deflectioneffect refers to the ratio of the intensity of the zero-order deflectedlight (the output light without changing the propagation direction) tothe intensity of the non-zero-order deflected light (the output lightchanged the propagation direction) is lower than 100. When the lightpassing through the ordinary region at a specific direction, lowdeflection effect will be generated, and the luminous flux is increased.Low deflection effect refers to the ratio of the intensity of thezero-order deflected light (the output light without changing thepropagation direction) to the intensity of the non-zero-order deflectedlight (the output light changed the propagation direction) is higherthan 100. In another embodiment, the same effect can be achieved whenthe ordinary region (or the non-light-deflection region) is anon-translucent region which almost allows no light to pass through.

Refer to FIG. 1B. The optical element 20 has a first pattern including aplurality of light deflection regions formed by way of engraving,embossing, transferring or printing. The first pattern refers to thedistribution pattern of the light deflection regions. The first patterncan have many implementations, but only four are exemplified below forillustration. In the first implementation (1), the light deflectionregions are uniformly distributed over the entire optical element 20,that is, the first pattern 21 a is equivalent to the size of the opticalelement 20. In the second implementation (2), the light deflectionregions are distributed on the central region of the optical element 20and form a non-light-deflection region on the boundary of the opticalelement 20, that is, the first pattern 21 b is smaller than the size ofthe optical element 20. In the third implementation (3), the firstpattern 21 c is smaller than the size of the optical element 20 in onedirection (such as the direction parallel to the Y axis as indicated inFIG. 1B) and two or more than two sets of first patterns can be arrangedat intervals from one another along the said direction in a periodicmanner. In the fourth implementation (4), the first pattern 21 d issmaller than the size of the optical element 20 in two directions (suchas the direction parallel to the X axis and the direction parallel tothe Y axis) and two or more than two sets of first patterns can bearranged at intervals from one another along one of the two directionsin a periodic manner. To summarize, the light deflection regions occupy30-100% of the area of the optical element 20. In an embodiment, thelight deflection regions occupy more than 90% of the area of the opticalelement 20. For example, the light deflection regions occupy 95-100% ofthe area of the optical element 20. It should be noted that, the borderline of the first pattern can be a straight line or a waveform curve,and only the waveform track is exemplified in implementations (2)-(4).

In an embodiment, the light deflection regions of the first pattern canbe arranged according to a periodic function in a first direction, thatis, the light deflection regions are arranged along at least oneperiodic track. In another embodiment, the light deflection regions ofthe first pattern are not only arranged according to a first periodicfunction in the first direction but also arranged according to a secondperiodic function in a second direction different from the firstdirection. That is, the light deflection regions are arranged at theintersection between two periodic tracks. The periodic function can beexemplified by a waveform function. For example, the light deflectionregions can be arranged along a first waveform track in a directionparallel to the X axis, wherein the first waveform track has a fixedperiod T₁ and a fixed amplitude A₁ perpendicular to the X axisdirection. In another embodiment, the light deflection regions not onlycan be arranged along the first waveform track in a direction parallelto the X axis but also arranged along a second waveform track in adirection parallel to the Y axis, wherein the second waveform track hasa fixed period T₂ and a fixed amplitude A₂ perpendicular to the Y axisdirection. However, the first waveform track and the second waveformtrack can have variable periods or variable amplitudes, and theinvention does not have specific restrictions thereto.

Possible arrangements of the light deflection regions are describedbelow with accompanying drawings. Referring to FIGS. 2A and 3A,exemplary arrangements of some light deflection regions 22 on theoptical element 20 are illustrated, wherein the blank part refers to thepart which the light deflection regions 22 are omitted or refers to thenon-light deflection region without deflection effect. Specifically, theoptical element 20 has many light deflection regions 22 and 24, and thefirst pattern is formed by the light deflection regions 22 and 24. Eachlight deflection region can be a circle, an eclipse or a polygon such astriangle, square, pentagon or hexagon. The light deflection regions havea characteristic dimension D1. If the light deflection regions form acircle, the characteristic dimension D1 is defined as a diameter. If thelight deflection regions form a polygon, the characteristic dimension D1is defined as a diameter of a circumcircle of the polygon. If the lightdeflection regions form an ellipse, the characteristic dimension D1 isdefined as an arithmetic average of a long axis and a short axis. Inother embodiments, based on the shape of the light deflection regions,the definition of the characteristic dimension can be adopted from asimilar shape. In an embodiment, the characteristic dimension D1 canrange from 4 to 80 μm, such as 30 to 60 μm or 20 to 70 μm. The lightdeflection regions can occupy 30%-100% of the area of the opticalelement.

In an embodiment as indicated in FIGS. 2A and 2B, the light deflectionregions 22 are arranged along a track 23 in a first direction (e.g. thedirection of the directional angle ψ=0 or the direction parallel to theX axis). The track 23 is a waveform track having a first period T₁ and afirst amplitude A₁, wherein the direction of first period is parallel tothe first direction (the direction parallel to the X axis), thedirection of first amplitude is perpendicular to the first direction(the direction perpendicular to the X axis). Here, the first period T₁refers to the distance from crest to crest (or trough to trough), andthe first amplitude A₁ refers to the distance from balance point tocrest or trough and is equivalent to a half of the distance from crestto trough. The track 23 can be expressed as:

$Y_{1} = {A_{1}{{\sin\left( {2\pi\frac{X_{1}}{T_{1}}} \right)}.}}$In an embodiment, the first amplitude A₁ and the first period T₁ can belarger than or equivalent to two times of the characteristic dimensionD₁ of the light deflection regions 22, that is, A₁≥2D₁ and T₁≥2D₁.Besides, the ratio of the first amplitude A₁ to the first period T₁ canbe larger than 0 but smaller than 10, that is,

$0 < \frac{A_{1}}{T_{1}} \leqq 10.$In another embodiment, A₁≥5D₁ and T₁≥10D₁. For example, the diameter D₁of the circular light deflection regions 22 as indicated in FIGS. 2A and2B is equivalent to 30 micro meters (μm), the first amplitude A₁ isequivalent to 1 millimeters (mm), and the first period T₁ is equivalentto 1 mm. In the present embodiment, the light deflection regions 22 arearranged along a straight line in a second direction (such as thedirection of the directional angle ψ=90° or the direction parallel tothe Y axis).

In another embodiment as indicated in FIGS. 3A and 3B, the lightdeflection regions 22 and 24 are arranged along a track 23 in a firstdirection (e.g. the direction of the directional angle ψ=0 or thedirection parallel to the X axis) and are also arranged along a track 25in a second direction (e.g. the direction of the directional angle ψ=90or the direction parallel to the Y axis). That is, the light deflectionregions 22 and 24 are arranged at the intersection between the track 23and the track 25. The track 25 is a waveform track having a secondperiod T₂ and a second amplitude A₂, wherein the direction of secondperiod is parallel to the second direction (the direction parallel tothe Y axis), and the direction of second amplitude is perpendicular tothe second direction (the direction perpendicular to the Y axis). Here,the second period T₂ refers to the distance from crest to crest (ortrough to trough), and the second amplitude A₂ refers to the distancefrom balance point to crest or trough and is equivalent to a half of thedistance from crest to trough. The track 25 can be expressed as:

$Y_{2} = {A_{2}{{\sin\left( {2\pi\frac{X_{2}}{T_{2}}} \right)}.}}$In an embodiment, the second amplitude A₂ and the second period T₂ canbe larger than or equivalent to two times of the characteristicdimensions D₁ of the light deflection regions 22 and 24, that is, A₂≥2D₁and T₂≥2D₁. Besides, the ratio of the second amplitude A₂ to the secondperiod T₂ can be larger than 0 but smaller than 1, that is,

$0 < \frac{A_{2}}{T_{2}} \leqq 1.$For example, the diameter D₁ of the circular light deflection regions 22as indicated in FIGS. 3A and 3B is equivalent to 30 μm, the firstamplitude A₁ is equivalent to 1 mm, the first period T₁ is equivalent to1 mm, the second amplitude A₂ is equivalent to 0.1 mm, and the secondperiod T₂ is 3 mm. In an embodiment, the ratio of the first amplitude A₁to the first period T₁ is larger than the ratio of the second amplitudeA₂ to the second period T₂, that is,

$\frac{A_{1}}{T_{1}} > {\frac{A_{2}}{T_{2}}.}$The track 23 having the period T₁ and the amplitude A₁ gets steeper withthe larger value of

$\frac{A_{1}}{T_{1}};$me track 25 having the period T₂ and the amplitude A₂ gets smoother withthe smaller the value of

$\frac{A_{2}}{T_{2}}.$

In an embodiment, the light deflection regions are arranged along thetrack 23 in the direction of the directional angle ψ=0±20° and are alsoarranged along the track 25 in the direction of the directional angleψ=90±20°. That is, the track 23 and the track 25 have differentdirections, and the included angle formed by the track 23 and the track25 can range from 50 to 130°. In another embodiment, the lightdeflection regions are arranged along the track 23 in the direction ofthe directional angle ψ=45±30° and are also arranged along the track 25in the direction of the directional angle ψ=135±30°. That is, theincluded angle formed by the track 23 and the track 25 can range from 30to 150°. Based on actual needs, the display device 1 of the inventioncan adjust the directional angles of the track 23 and 25 of the firstpattern formed on the optical element 20 to generate differentdeflection effects.

In an embodiment, the track 23 is, for example, a sine function or anapproximate sine function, and may include many types of periodicfunctions. The periodic functions are not limited to one, and can be asum of different periodic functions. If the function of the track 23 isa sum of multiple periodic functions having the same period, the periodof the track 23 is still the same. If the function of the track 23 is asum of multiple periodic functions having different periods, the periodof the track 23 is the least common multiple of the periods of themultiple periodic functions. For example, a function having a period of6π can be produced by the sum of the function having a period of 2π andthe function having a period of 37π. The function of the track 25 can beobtained by the same analogy, and the similarities are not repeatedhere. Thus, the track 23 and the track 25 can be obtained from theperiodic functions having the same period or having different periods.Let a Fourier series f(t) be taken for example. The Fourier series f(t)is composed of sine functions and/or cosine functions, and can beexpressed as:

${{f(t)} = {a_{0} + {\sum\limits_{n = 1}^{\infty}\left( {{a_{n}\cos\;({nt})} + {b_{n}\sin\;({nt})}} \right)}}},\mspace{11mu}{{- \pi} \leq t \leq \pi}$Wherein, t ∈[−π, π], a_(n) and b_(n) represent amplitudes.

To simplify the drawing, the following drawing illustrates only patternsformed of a part of the light deflection regions. In an embodiment asindicated in FIG. 4A, eight circular light deflection regions 32 aretaken for illustration. The eight circular light deflection regions 32are arranged into two adjacent groups with each group having fourcircular light deflection regions along a track 33 in a first direction(the directional angle ψ=0), and are arranged into four adjacent groupswith each group having two circular light deflection regions along astraight line M in a second direction (the directional angle ψ=90). Thetwo tracks 33 are arranged with a first pitch P₁ in the seconddirection, and four straight lines M are arranged with a second pitch P₂in the first direction.

In another embodiment as indicated in FIG. 4B, eight square lightdeflection regions 36 are taken for illustration. The eight square lightdeflection regions 36 are arranged into two adjacent groups with eachgroup having four square light deflection regions along a track 33 in afirst direction (the directional angle ψ=0), and are arranged into fouradjacent groups with each group having two square light deflectionregions along a straight line M in a second direction (the directionalangle ψ=70). The two tracks 33 are arranged with a first pitch P₁ in thesecond direction, and the four straight lines M are arranged with asecond pitch P₂ in the first direction.

As disclosed in above embodiments, the light deflection regions arearranged along the first track in the first direction and arranged alongthe second track in the second direction. The first tracks are arrangedwith the first pitch P₁, that is, the first pitch P₁ refers to thedistance between two closest first tracks, and the relationship betweenthe first pitch P₁ and the characteristic dimension D₁ of lightdeflection regions can be expressed as: 0.1D₁≤P₁≤25D₁. Besides, thesecond tracks are arranged with the second pitch P₂, that is, the secondpitch P₂ refers to the distance between two closest second tracks, andthe relationship between the second pitch P₂ and the characteristicdimension D₁ of the light deflection regions can be expressed as:0.1D₁≤P₂≤25D₁. In other embodiments, the ratio of the first pitch P₁ tothe second pitch P₂ can be larger than or equivalent to 0.1, but smallerthan or equivalent to 10, that is,

$0.1 \leqq \;\frac{P_{1}}{P_{2}} \leqq 10.$As disclosed in above embodiments, the relationship between the firstpitch P₁ and the characteristic dimension D₁ of the light deflectionregions can be expressed as: 0.5D₁≤P₁≤10D₁; the relationship between thesecond pitch P₂ and the characteristic dimension D₁ of the lightdeflection regions can be expressed as: 0.5D₁≤P₂≤10D₁. In theembodiments with more than two groups of the light deflection regions,the values of the first pitch P₁ and the second pitch P₂ can be fixed orvariant, and can be adjusted according to actual needs. The concepts ofpitches disclosed below are similar to that of the above embodiments,and the similarities are not repeated.

Even if the circular light deflection regions 32 are stacking with theperiodically arranged pixel structures, there are misplacements betweensome of the circular light deflection regions 32 and the pixelstructures (the locations are not corresponding), for the circular lightdeflection regions 32 are arranged along the track 33. Therefore, themoiré interference pattern (or ghost image) which affects the displayquality will not be generated easily. Refer to FIG. 4B. The square lightdeflection regions 36 arranged along the tracks 33 also have theanti-interference effect. The anti-interference effect of the followingembodiments is similar to that of the above embodiments, and thesimilarities are not repeated.

Refer to FIG. 5A, ten circular light deflection regions 32 are taken forillustration. The embodiment of FIG. 5A is different from that of FIG.4A in that: the circular light deflection regions 32 are arranged intotwo adjacent groups with each group having five circular lightdeflection regions along a track 33 in a first direction (thedirectional angle ψ=0) and are arranged into five adjacent groups witheach group having two circular light deflection regions along a track 35in a second direction (the directional angle ψ=70), the included anglebetween the track 33 and track 35 can range from 30 to 150°, and theratio of the first pitch P₁ to the second pitch P₂ can be larger than orequivalent to 0.1 but smaller than or equivalent to 10, that is,

$0.1 \leqq \;\frac{P_{1}}{P_{2}} \leqq 10.$In the present embodiment, the relationship between the first pitch P₁and the characteristic dimension D₁ of the light deflection regions canbe expressed as: 1.1D₁≤P₁≤20D₁; the relationship between the secondpitch P₂ and the characteristic dimension D₁ of the light deflectionregions can be expressed as: 1.1D₁≤P₂≤20D₁, and the light deflectionregions 32 are mutually separated without overlapping each other. Referto FIG. 5B. The arrangement of the square light deflection regions 36along the tracks 33 and 35 can be similar to the above arrangement.

In an embodiment, when the value of

$\frac{P_{1}}{D_{1}}$is smaller than 1 and/or the value of

$\frac{P_{2}}{D_{1}}$is smaller than 1, this implies that at least two groups of the circularlight deflection regions 32 partly overlap with each other. When twogroups of the circular light deflection regions 32 partly overlap witheach other, the deflection effect of the overlapped part may bedifferent from that of the non-overlapped part because the overlappedpart and the non-overlapped part may have different patterns (that is, afirst pattern and a second pattern having different shapes or differentconditions). For example, by stacking two films of the optical element20 together, one group of the circular light deflection regions 32 ofthe first pattern at least partly overlaps one group of the circularlight deflection regions 32 of the second pattern. When a stackedstructure formed of multilayers of optical element 20 is irradiated by alight source, a penetrating light will be generated in the deflectingdirection of single layer of the optical element 20 as well as otherdeflecting directions (such as oblique directions), and the deflectioneffect can therefore be enhanced.

Refer to FIG. 6A. Let 12 circular light deflection regions 42 a, 42 band 42 c be taken for illustration. The 4 circular light deflectionregions 42 a, the 4 circular light deflection regions 42 b and the 4circular light deflection regions 42 c are arranged as three rows witheach row having four circular light deflection regions along threetracks 43 a in a first direction (the directional angle ψ=0) and arearranged as four columns with each column having three circular lightdeflection regions along four straight lines M in a second direction(the directional angle ψ=90). Tracks 43 a are arranged with a firstpitch P₁, and straight lines M are arranged with a second pitch P₂. Itshould be noted that the light deflection regions 42 a, 42 b and 42 ccan have the same or different sizes or shapes, and a circular shape istaken for illustration in the present embodiment. The light deflectionregions 42 a, 42 b and 42 c can be arranged along the same or differenttracks in the first direction and the second direction respectively, andidentical tracks 43 a and identical straight lines M are taken forillustration in the present embodiment. The light deflection regions 42a, 42 b and 42 c can be mutually separated or at least partly overlappedwith each other. In the present embodiment, the light deflection regions42 a and the light deflection regions 42 b at least partly overlap witheach other, and the light deflection regions 42 b and the lightdeflection regions 42 c at least partly overlap with each other, whereinthe light deflection regions 42 b are located between the lightdeflection regions 42 a and the light deflection regions 42 c. In thepresent embodiment, the first pitch P₁ between two adjacent tracks 43 ais smaller than the characteristic dimension D₁ (P₁<D₁), and the lightdeflection regions along each track 43 a at least partly overlap witheach other. In another embodiment, both the first pitch P₁ between twoadjacent tracks 43 a and the second pitch P₂ between two adjacentstraight lines M are smaller than the characteristic dimension D₁ (P₁<D₁and P₂<D₁), such that both the light deflection regions along each track43 a and the light deflection regions along each straight line M atleast partly overlap with each other. Here, the light deflection regionscan be formed on a single optical layer. In another embodiment, thelight deflection regions can be light deflection regions on multilayeredstructure formed of multiple layers (two or more than two layers) of theoptical element 20 stacked together. For example, the light deflectionregions 42 a and the light deflection regions 42 c are located on a filmof the optical element 20 to form the first pattern, and the lightdeflection regions 42 b are located on the other film of the opticalelement 20 to form the second pattern, and the first pattern and thesecond pattern may have the same or different tracks.

Referring to FIG. 6B, two types of light deflection regions 42 a and 42b are exemplified for illustration. The light deflection regions 42 aare arranged as two adjacent rows with each row having four lightdeflection regions 42 a along a track 43 a in a first direction (thedirectional angle ψ=0) and are arranged as four adjacent columns witheach column having two light deflection regions 42 a along a track 45 ain a second direction (the directional angle ψ=90). The light deflectionregions 42 b are arranged as two adjacent rows with each row havingthree light deflection regions along a track 43 b in the first direction(the directional angle ψ=0), and are arranged as three adjacent columnswith each column having two light deflection regions along a track 45 bin the second direction (the directional angle ψ=90). Every two adjacenttracks 43 a are separated by a first pitch P₁, every two adjacent tracks45 a are separated by a second pitch P₂, every two adjacent tracks 43 bare separated by a third pitch P₃, and every two adjacent tracks 45 bare separated by a fourth pitch P₄. In an embodiment, the first pitch P₁is different from the third pitch P₃, and/or the second pitch P₂ isdifferent from the fourth pitch P₄. In an embodiment, the characteristicdimension D₂ of the light deflection regions 42 b is larger than orsmaller than the characteristic dimension D₁ of the light deflectionregions 42 a. In another embodiment, the characteristic dimension D₂ ofthe light deflection regions 42 b is equivalent to the characteristicdimension D₁ of the light deflection regions 42 a. Whether the lightdeflection regions 42 a and 42 b are mutually separated or at leastpartly overlap with each other can be determined according to therelative relationship between the pitches P₁, P₂, P₃ and P₄ and thecharacteristic dimensions D₁ and D₂. For example, when the first pitchP₁ and/or the third pitch P₃ is smaller than D₁+D₂ or when the secondpitch P₂ and/or the fourth pitch P₄ is smaller than D₁, the lightdeflection regions may partly overlap with each other. Here, the lightdeflection regions can be formed on a single optical layer. In anotherembodiment, the light deflection regions can be light deflection regionson multilayered structure formed of multiple layers (two or more thantwo layers) of the optical element 20 stacked together. For example, thelight deflection regions 42 a are located on a film of the opticalelement 20 to form the first pattern, and the light deflection regions42 b are located on the other film of the optical element 20 to form thesecond pattern, wherein the first pattern and the second pattern mayhave the same or different tracks.

The light deflection regions can be realized by diffraction structureshaving deflection effect and are exemplified below. The light deflectionregions may include a diffraction structure having a single period.Refer to FIG. 7A. The light deflection regions 52 include a diffractionstructure 53 a having a single period. For example, the diffractionstructure 53 a is a grating structure having a single period. The lightdeflection regions may include a diffraction structure having variantperiods (also referred as “multiple periods”), that is, the diffractionstructure may include a grating structure having two or more than twoperiods. Refer to FIGS. 7B-7E. The diffraction structures 53 b-53 e aregrating structures having multiple periods, and the grating periodsrange from 0.4 to 10 μm.

In an embodiment, the diffraction structure of the light deflectionregions include at least two grating groups with each group having atleast one grating unit, and the grating units in the same grating grouphave the same grating period. If the largest grating period of eachgrating group of the diffraction structure is defined as C, then thevariation of the grating period between two closest grating groups isequivalent to at least 1% of the largest grating period C or is smallerthan 90% of the largest grating period C. For example, if the largestgrating period is equivalent to 2 μm, then the variation of the gratingperiod between two closest grating groups is equivalent to at least 0.02μm or is smaller than 1.8 μm. In another embodiment, if the variationbetween the largest grating period and the smallest grating period ofthe diffraction structure is defined as ΔC, then the variation of thegrating period between two closest grating groups ranges from 5% to 100%of the variation ΔC. For example, if the variation ΔC between thelargest grating period and the smallest grating period is equivalent to1.2 μm, then the variation of the grating period between two closestgrating groups is equivalent to 0.06-1.2 μm.

Four implementations of the light deflection regions as illustrated inFIGS. 7B˜7E and are described below. In the present embodiment, thegrating unit is exemplified by strip-shaped grating bars. As indicatedin FIG. 7B, the light deflection region 52 has 20 grating groups witheach group having a grating bar, and the grating groups are arranged toform a diffraction structure 53 b having gradient periods in a singledirection. For example, the grating periods progressively increase tothe second period T₆ (such as 2.0 μm) from the first period T₅ (such as0.8 μm) to form a diffraction structure 53 b whose grating units havedecreasing densities. In the present embodiment, since each grating barhas a different grating period, the grating periods are defined asgradient periods. As indicated in FIG. 7C, the diffraction structure 53c of the light deflection regions 52 has three grating groups eachhaving 3-6 grating bars, and the grating periods of the grating groupsprogressively increase in a single direction. For example, the gratingperiods can progressively increase to the second period T₆ (such as 1.3μm) from the first period T₅ (such as 0.8 μm), and then furtherprogressively increase to the third period T₇ (such as 2.0 μm) from thesecond period T₆ to form a diffraction structure 53 c whose gratingunits have decreasing densities. As indicated in FIG. 7D, the lightdeflection regions 52 has 10 grating groups each having one grating bar,and the grating groups are arranged to form a diffraction structure 53 dhaving bilateral gradient periods. For example, the grating periods canprogressively decrease to the second period T₆ (such as 0.8 μm) from thefirst period T₅ (such as 2.0 μm), and then progressively increase to thethird period T₇ (such as 2.0 or 1.3 μm) from the second period T₆ toform a diffraction structure 53 d whose grating units have increasingdensities first and then have decreasing densities, wherein the densityis higher at the middle part but lower at the two lateral sides. Asindicated in FIG. 7E, the light deflection regions 52 has 10 gratinggroup each having one grating, and the grating groups are arranged toform a diffraction structure 53 e having bilateral gradient periods. Forexample, the grating periods can progressively increase to the secondperiod T₆ (such as 2.0 μm) from the first period T₅ (such as 0.8 μm),and then progressively decrease to the third period T₇ (such as 0.8 or1.3 μm) from the second period T₆ to form a diffraction structure 53 e,wherein the density is lower at the middle part but higher at the twolateral sides.

In comparison to the diffraction structure 53 a arranged according toone single period, the diffraction structures 53 b-53 e of the presentembodiments have variant periods, and are less likely to generateinterfering moiré pattern (or ghost image) and will not affect thedisplay effect.

In other embodiments, the problem of moiré pattern can be resolved byadjusting the ratio of grating period to amplitude. As disclosed above,the diffraction structure of the light deflection regions may includemultiple grating units having different grating periods. The relationbetween the grating period and the amplitude is described below usingthe diffraction structure having gradient periods. Refer to FIGS. 8A and8B, side views of diffraction structures 63 a and 63 b having gradientperiods (or gradient density) and gradient amplitudes are shown. Asindicated in FIG. 8A, when the periods of the grating units of thediffraction structure 63 a progressively decrease towards the twolateral sides from the central region of the diffraction structure 63 a,the amplitudes of the grating units may progressively decrease towardsthe two lateral sides from the central region of the diffractionstructure 63 a. As indicated in FIG. 8B, when the periods of the gratingunits of the diffraction structure 63 b progressively increase towardsthe two lateral sides from the central region of the diffractionstructure 63 b, the amplitudes of the grating units may progressivelyincrease towards the two lateral sides from the diffraction structure 63b. Designations w₁ and h₁ respectively denote the period and theamplitude of the grating units at the central region of the diffractionstructures 63 a and 63 b, and designations w₂ and h₂ respectively denotethe amplitude of the grating units near the two lateral sides. In thetwo embodiments disclosed above, the period w₁ of the grating units atthe central region can be larger than or smaller than towards the periodw₂ of the grating units near the two lateral sides, that is, w₁>w₂ orw₁<w₂. Furthermore, the amplitude h₁ of the grating units at the centralregion can be larger than or smaller than the amplitude h₂ of thegrating units near the two lateral sides, that is, h₁>h₂ or h₁<h₂. In anembodiment, the aspect ratio of the grating units at the central regionis equivalent to the ratio of the amplitude h₁ to the period w₁, and mayrange from 0.1 to 10; the aspect ratio of the grating units near the twolateral sides is equivalent to the ratio of the amplitude h₂ to theperiod w₂, and may range from 0.1 to 10. When the value of

$\frac{h_{1}}{w_{1}}$is equivalent to that of

$\frac{h_{2}}{w_{2}},$this implies that both the periods and the amplitudes of the gratingunits of the diffraction structures 63 a and 63 b vary proportionallyand progressively (such as progressively increase or progressivelydecrease) towards the two lateral sides from the central region. Thus,the deflection effect of the diffraction structures 63 a and 63 b can bechanged by changing the periods and the amplitudes of the grating units.

Refer to FIG. 8C. The periods and the amplitudes of the grating units ofthe diffraction structure 63 c may vary progressively from one sidetowards the other side of the diffraction structure 63 c. In anembodiment, the value of

$\frac{h_{1}}{w_{1}}$is equivalent to 0.5, and the value of

$\frac{h_{2}}{w_{2}}$is equivalent to 0.5. When the value of

$\frac{h_{1}}{w_{1}}$is equivalent to that of

$\frac{h_{2}}{w_{2}},$this implies that the periods and the amplitudes of the grating units ofthe diffraction structure 63 c vary proportionally and progressively(such as progressively increase or progressively decrease) from one sidetowards the other side of the diffraction structure 63 c. Thus, thedeflection effect of the diffraction structure 63 c can be changed bychanging the periods and the amplitudes of the grating units.

Refer to FIGS. 9A to 9D. FIG. 9A is a FWHM (full width at half maximum)diagram of a square waveform diffraction structure 72 a. FIG. 9B is aFWHM diagram of a serrated waveform diffraction structure 72 b. FIG. 9Cis a FWHM diagram of a sine waveform diffraction structure 72 c. FIG. 9Dis a FWHM diagram of an obliquely serrated waveform diffractionstructure 72 d. Designation T_(g) denote the period of the diffractionstructure having a single period, and designation w denote the width(that is, the FWHM width) at which the amplitude is equivalent to ½ ofthe height. In an embodiment, the ratio of the FWHM w to the periodT_(g) can range from 0.1 to 0.9. Thus, the deflection effect of thediffraction structure can be changed by changing the waveform and theFWHM width of the diffraction structure.

According to the optical element and the display device using the samedisclosed in above embodiments of the invention, the light deflectionregions arranged along the waveform track, the moiré pattern generateddue to periodic arrangement can be eliminated without affecting thedisplay effect of the display device. Moreover, the diffractionstructure having variant periods can also eliminate the moiré patterngenerated due to periodic arrangement without affecting the displayeffect of the display device.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodiments.It is intended that the specification and examples be considered asexemplary only, with a true scope of the disclosure being indicated bythe following claims and their equivalents.

What is claimed is:
 1. An optical element, comprising: a first pattern,comprising: a plurality of light deflection regions arranged along atleast one set of first tracks in a first direction, wherein each firsttrack is a waveform track having a first period T₁ and a first amplitudeA₁, wherein the light deflection regions have a characteristic dimensionD, and T₁, A₁ and D satisfy the following expressions: $\begin{matrix}{{A_{1} \geqq {2D}};} & (1) \\{{T_{1} \geqq {2D}};{and}} & (2) \\{0 < \frac{A_{1}}{T_{1}} \leqq 10.} & (3)\end{matrix}$
 2. The optical element according to claim 1, wherein eachfirst track is a sine function or a Fourier series represented as thesum of a plurality of sine functions.
 3. The optical element accordingto claim 1, wherein the light deflection regions are arranged along atleast one set of second tracks in a second direction different from thefirst direction.
 4. The optical element according to claim 3, whereineach second track is a straight line.
 5. The optical element accordingto claim 3, wherein each second track is a waveform track having asecond period T₂ and a second amplitude A₂.
 6. The optical elementaccording to claim 5, wherein each second track is a sine function or aFourier series represented as the sum of a plurality of sine functions,and T₂, A₂ and a characteristic dimension D of the light deflectionregions satisfy the following expressions: $\begin{matrix}{{A_{2} \geqq {2D}};} & (1) \\{{T_{2} \geqq {2D}};{and}} & (2) \\{0 < \frac{A_{2}}{T_{2}} \leqq 1.} & (3)\end{matrix}$
 7. The optical element according to claim 6, wherein$\frac{A_{1}}{T_{1}} > {\frac{A_{2}}{T_{2}}.}$
 8. The optical elementaccording to claim 3, wherein the first tracks are arranged with a firstpitch P₁ in the second direction, and 0.1D≤P₁≤25D; and the second tracksare arranged with a second pitch P₂ in the first direction, and0.1D≤P₂≤25D.
 9. The optical element according to claim 8, wherein$0.1 \leqq \frac{P_{1}}{P_{2}} \leqq 10.$
 10. The optical elementaccording to claim 1, wherein each of the light deflection regionscomprises a diffraction structure having two or more than two types ofperiods.
 11. The optical element according to claim 1, wherein each ofthe light deflection regions comprises a diffraction structure havingtwo or more than two types of amplitudes.
 12. The optical elementaccording to claim 1, wherein each of the light deflection regionscomprises a diffraction structure arranged according to at least one ofa gradient period and a gradient amplitude.
 13. A display device,comprising: a display; and the optical element according to claim 1disposed on a light output surface of the display.
 14. An opticalelement, comprising: a film; and a plurality of light deflection regionsarranged on the film, wherein each light deflection region comprises adiffraction structure having two or more than two types of periods,wherein the diffraction structure include at least two grating groups,and a variation of the grating period between two closest grating groupsranges from 5% to 100% of the variation ΔC, wherein the ΔC is avariation between a largest grating period and a smallest grating periodof the diffraction structure.
 15. The optical element according to claim14, wherein each of the light deflection regions comprises a diffractionstructure having two or more than two types of amplitudes.
 16. Theoptical element according to claim 14, wherein each of the lightdeflection region comprises a diffraction structure arranged accordingto at least one of a gradient period and a gradient amplitude.
 17. Adisplay device, comprising: a display; and the optical element accordingto claim 14 disposed on a light output surface of the display.
 18. Anoptical element, comprising: a film; and a plurality of light deflectionregions arranged on the film, wherein each light deflection regioncomprises a diffraction structure having two or more than two types ofperiods, wherein the diffraction structure include at least two gratinggroups, and a variation of the grating period between two closestgrating groups is equivalent to at least 1% of the largest gratingperiod C or is smaller than 90% of the largest grating period C.